1. Field of the Invention
The present invention relates to a media mixing mill. The media mixing mill is particularly suitably used, but not limited to, to mix a target material, such as ink, paint, pigment, ceramics, metal, inorganics, dielectrics, ferrite, toner, glass or paper coating color, with grinding media, to pulverize the material into fine particles or disperse the material.
2. Description of the Background Art
The media mixing mill of the present invention is one type of media agitating mill. The media agitating mill is widely used in the field of fine grinding, such as dispersion of ink or paint, pulverization/dispersion of ceramics, pulverization/dispersion of metal or inorganics, and pulverization/dispersion of medicinal drug, and various types of media agitating mills are already known.
Heretofore, the media agitating mill has been configured such that a target material and grinding media are agitated together using an agitating member provided inside a grinding container, to pulverize the target material, and the pulverized material and the grinding media are separated from each other through a separator provided at an end of a flow of the pulverized material, in such a manner as to allow only the pulverized material to be discharged from inside a grinding container.
This type of media agitating mill is essentially required to have the separator for separating a pulverized material from grinding media. As the separator, a type having a mechanical separation mechanism, such as a gap type or a screen type, has been employed.
However, in reality, the separator having a mechanical separation mechanism inevitably involves a trouble, such as blockage or clogging, which jeopardizes a stable continuous operation.
With a view to solving the problem with the above separator, there has been proposed a media agitating mill (grinder or pulverizer) comprising an agitating/separating member adapted to apply a centrifugal force to grinding media and a target material so as to agitate them and pulverize the target material, and simultaneously separate the pulverized material from the grinding media by means of a balance between the centrifugal force and a drag force of a fluid being transporting the pulverized material in a direction opposite to a direction of the application of the centrifugal force (see, for example, the following Patent Document 1).
[Patent Document 1] JP 2003-144950A
However, in the above media agitating mill (pulverizer), the agitating/separating member is costly due to its complicate structure which comprises front and rear circular disks disposed in opposed relation to each other with a given distance therebetween in an axial direction of a rotary shaft, and a plurality of blade plates integrally provided across the circular disks and arranged at even intervals in a circumferential direction of the circular disks. The agitating/separating member is significantly worn away depending on a type of target material. In this case, a cost for replacement of the agitating/separating member will be excessively increased. Moreover, the above media agitating mill (pulverizer) is adapted to adjustably change a shape of an inner peripheral surface of a grinding tank in order to cope with diversification of target materials, and thereby it is necessary to prepare a large number of the costly agitating/separating members corresponding to various shapes of the inner peripheral surface of the grinding tank, which accelerates an increase in cost.
As measures against the above problem, in JP 2005-199125A, there has been proposed a media agitating mill which comprises a low-cost agitating/separating member having a simple structure and allowing for stable pulverization and dispersion without a trouble, such as blockage or clogging.
Specifically, the media agitating mill proposed in the JP 2005-199125A comprises a grinding tank having grinding chamber defined thereinside to receive therein grinding media, a rotary shaft rotatably installed in the grinding tank, and an agitating/separating member provided to the rotary shaft in a position located inside the grinding chamber and adapted to be integrally rotatable together with the rotary shaft, wherein an outer peripheral surface of the agitating/separating member is formed in a shape conformable to that of an inner wall surface of the grinding chamber. The media agitating mill further has a separation/discharge passage penetratingly extending from the outer peripheral surface to a central portion of the agitating/separating member and then penetratingly extending from the central portion through a central portion of the rotary shaft so as to communicate with an outside of the grinding chamber, and a pressure reduction hole penetrating between upper and lower surfaces of the agitating/separating member in an axial direction of the rotary member so as to communicate between upper and lower regions of an internal space of the grinding chamber.
[Patent Document 2] JP 2005-199125A
However, in the above media agitating mill, the grinding media are apt to be locally concentrated in a maximum-diameter region where a centrifugal force is maximized, and thereby a dispersion or pulverization force will vary depending on position with a large difference therein. Thus, there is a problem of being unable to uniformly perform dispersion or pulverization of a target material to cause difficulty in obtaining a high-quality product.